1. Field of the Invention
The present invention relates to an information card system and particularly relates to an information card system which writes information on the card in a non-contact manner.
2. Prior Art
An example of a conventional information card reader which reads information from an information card is illustrated in FIG. 1. In an information card reader 1, an interrogation, or, response requiring, signal W1 using a microwave frequency of 2.45 GHz, for example, as a carrier, is generated in a response requiring signal generating circuit 2 and is broadcast from a transmission antenna 3 to an information card 4. A response information signal W2 which is returned from the information card 4 is received in a response signal processing circuit 6 through a receiving antenna 5. In this manner, the information card reading system may be used for detecting visitors who have no information card 4 as an identification card or checking freight with the information card 4 as a tag.
Japanese Patent (unexamined) Laid-open No. 1 (1989)-182782 proposes that the information card 4 which is used in such an information card reading system comprise a dipole antenna 4B, an information signal generating circuit 4C and a power supply battery 4D which are connected by a wiring pattern 4E. The dipole antenna 4B is mounted on the wiring board 4A to form part of the wiring pattern, and the information signal generating circuit 4C has an integrated circuit (IC) structure. The dipole antenna 4B changes its reflection ratio when responding to the carrier of the response requiring signal W1 broadcast from the information reader 1, by changing its impedance at a feeding point according to an information signal generated in the information signal generating circuit 4C, thereby making the reflected wave become the response information signal W2.
The information signal generating circuit 4C has an electrical circuit configuration as shown in FIG. 2. Information data S1 previously stored in an information memory 11, a PROM, for example, is read according to an address signal S3 of an address counter 13 which is actuated by a clock signal S2 of a clock signal generator 12, and the information data read is supplied to a variable impedance circuit 14 which is shown constituted by a field effect transistor.
The variable impedance circuit 14 is interconnected between a pair of feeding point terminals T1 and T2 to which the dipole antenna 4B is connected. Thus, impedance of the dipole antenna 4B at the feeding point is variably controlled by performing on-off actuation of the field effect transistor when the information data S1 changes between logic "1" or "0", thereby variably controlling the reflection ratio in respect to the response requiring signal W1 incident upon the dipole antenna 4B.
Interconnected between the earth side feeding point terminal T1 and a power supply terminal T3 of the information signal generating circuit 4C is a power supply battery 4D. This enables the variable control of the impedance at the feeding point of the dipole antenna 4B to be continuously effected in accordance with the information data S1.
A specific identification code is allotted to the information memory 11 of each information card 4, and hence information contained in each information card 4 identifies the respective information card.
To initialize, that is, write identification code information on, to the information card 4, it has been proposed to bring electrodes of a writer into contact with electrodes (not shown) of the information card 4. However, this method of writing information in a contact manner produces a problem in that during mass production of the information card, productivity is reduced due to the additional time required for effecting direct contact.
To overcome this problem it has been proposed to provide electrode plates, instead of a dipole antenna and contact electrodes, on an information card to send and receive information. The plates are placed in the vicinity of plates formed on a separate writer to produce an electric coupling between them for sending and receiving information in a non-contact manner (Japanese Patent (unexamined) Laid-open Publication 63 (1988)-39396). However, in both writing information on and reading information from the information card, the information card must be placed in the vicinity of the information reader since the information card uses the plates for writing and reading information. Thus, the information card is insufficient in its ease of use.